The energy design of a building is a multivariable problem for which there exists different sets of solutions. In this paper an integrated energy design process is proposed to support designers in identifying the most suitable set of passive solutions to guarantee a comfortable indoor environment and hence to minimize its energy needs for space conditioning. The proposed design process uses EnergyPlus as an energy simulation engine, guided by GenOpt via some code written by the authors. The optimization aims at minimizing two seasonal long-term discomfort indices (based on the ASHRAE Adaptive comfort model) through the Particle swarm optimization algorithm. The proposed process in a case study is tested here where we identify the most suitable envelope components and passive strategies for the design of a single-family net zero-energy home located in the Mediterranean climate. The building is currently under construction. It should be noted, however, that the modeling and the optimization approach outlined in this paper can be applied to any residential or commercial building prototype.